Technical Field
This disclosure relates to a photo sensor and a display device having the same, in particular to a photo sensor using thin film transistors and a display device having the same.
Description of the Related Art
A photo sensor is a device that stores amount of charge according to intensity of light as information and outputs the stored information according to an external control signal. The photo sensor is widely used as an image recognition device for reading characters and pictures in a X-ray detector, a scanner, a digital copier, a fingerprint recognition system, a facsimile or the like.
Hereinafter, a related art photo sensor (hereinafter, referred to as a “photo sensor”) using thin film transistors will be described with reference to FIG. 1 and FIG. 2.
FIG. 1 is a plan view showing an example of a related art photo sensor, and FIG. 2 is a cross-sectional view taken along line I-I′ of FIG. 1.
Referring to FIGS. 1 and 2, the photo sensor includes a switching thin film transistor (TFT) 20, a storage capacitor 30, and a sensor TFT 40.
The sensor TFT 40 includes a sensor drain electrode 41, a sensor source electrode 42, a sensor gate electrode 45, and a sensor semiconductor layer 47. The sensor gate electrode 45 is formed on the substrate 10, and the sensor semiconductor layer 47 is insulated from the sensor gate electrode 45 by a first insulating layer 51 covering the sensor gate electrode 45. The sensor drain electrode 41 and the sensor source electrode 42 are arranged to be in contact with the sensor semiconductor layer 47. The sensor drain electrode 41 is connected to a sensor drain wire 48, and the sensor gate electrode 45 is connected to a sensor gate line 46.
The switching TFT 20 includes a switching drain electrode 21, a switching source electrode 22, a switching gate electrode 25, and a switch semiconductor layer 27. The switching gate electrode 25 is formed on the substrate 10, and the switch semiconductor layer 27 is insulated from the switching gate electrode 25 by the first insulating layer 51 covering the switching gate electrode 25. The switching drain electrode 21 and the switching source electrode 22 are arranged to be in contact with the switch semiconductor layer 27. The switching source electrode 22 is connected to a lead-out wire 28, and the switching gate electrode 25 is connected to a switching gate line 26. The lead-out wire 28 functions as a data line through which charges stored in the storage capacitor 30 are output.
The storage capacitor 30 includes a first capacitor electrode 31 and a second capacitor electrode 32 that are insulated from each other by a first insulating layer 51. The first capacitor electrode 31 is formed integrally with the sensor gate electrode 45 and separated from the switching gate electrode 25 as shown in FIG. 2. The second capacitor electrode 32 is formed integrally with the sensor source electrode 42 and the switching drain electrode 21.
A second insulating layer 52 is stacked on the sensor TFT 40, the storage capacitor 30, and the switching TFT 20 to cover them. A light shielding film 29 is formed on the second insulating layer 52 in the region where the switching TFT 20 is formed. A protective film 53 is disposed on the second insulating layer 52 on which the light shielding film 29 is formed so as to cover the light-shielding film 29.
The sensor TFT 40 senses an input light to generate a current, and charges are accumulated in the storage capacitor 30 by the current generated by the sensor TFT 40. The stored charges are output to the lead-out wire 28 by a switching operation of the switching TFT 20.
In the above-described photo sensor, the first capacitor electrode 31 and the sensor gate electrode 45 are formed integrally, and the switching gate electrode 25 is formed to be separated from the first capacitor electrode 31 and the sensor gate electrode 45. In such a structure, since the switching gate line 26 have to be formed separately from the first capacitor electrode 31 and the sensor gate line 46. Therefore, there are some problems in that a space utilization is reduced, thereby reducing an integration of the photo sensor as well as an aperture ratio when the photo sensor is applied to a display device.